As the integrated circuit industry progresses, the number of devices required to be allocated inside a chip grows continuously, with repeated doubling, which makes the line width shrink and shrink, such that the photolithography imaging also must be finer and finer. Thus, the minimum size of the patterns on the integrated circuits is always a representative pointer in the development history of the semiconductor technology.
However, most of today's semiconductor technology uses conventional optical methods. Since the electromagnetic characteristics of optics, limits the exposure line width, if we want a finer line width, we must use a light source with a shorter wavelength. The wavelength of the light source used in today's semiconductor industry is as short as 248 nm. The wavelength of these light sources reaches the limits of interference in some advance processes and the more complex Phase Shifting Mask Method must be used to accommodate the light source being used in advanced deep sub-micron processes.
Thus, it is known that the photolithography process is associated with the line width being exposed. This means that for a finer line width, the photolithography process with a shorter wavelength is required to avoid the diffraction phenomena, and an exact pattern is acquired. So if the light source with the same wavelength is used to expose the devices with various line widths, the exact exposure in some regions could be acquired, with some exceptions that there is a diffraction phenomenon in some regions. In addition to the special characteristic of the general logic device product line which makes use of various pattern densities of a multi-layer pattern structure, due to the variation of products, such variation of the pattern density between layers will cause a line width change which does not obey the specification of the line width error. There is also a deference of the photolithography process in the process of the same product, i.e., it is required to change the condition of the photolithography in each process. So, the engineers use fine-tuning of the photolithography process to conform to the requirements of the products in most conventional processes, which also causes problems in mass production and makes the mass production line increasingly more complex.
Thus, the present invention is directed to overcoming the drawback caused by fine-tuning of the photolithography process and avoid the problems in mass production of the conventional logic devices.